1. Field of the Invention
The present invention relates to a process for producing a polybutadiene. More particularly, the present invention relates to a process for producing a cis-1,4-polybutadiene, a 1,2-polybutadiene having a desired vinyl content, a crystalline 1,2-polybutadiene or a polybutadiene containing crystalline 1,2-polybutadiene segments.
2. Description of the Related Art
The structure of a butadiene polymer composed mainly of 1,3-butadiene depends largely upon the catalyst system used in the production of the polymer. For example, it is known that a cis-1,4- or trans-1,4-polybutadiene is obtained when a catalyst system consisting of a transition metal compound and an alkylaluminum is used. It is also known that a syndiotactic 1,2-polybutadiene is obtained when a catalyst system consisting of CoBr.sub.2 (PPh.sub.3).sub.2, Al(C.sub.2 H.sub.5).sub.3 and water is used (Japanese Patent Application Kokoku No. 44-32426).
Meanwhile, it is known that when a catalyst system consisting of BuLi or Cr(acac).sub.3 --Al(C.sub.2 H.sub.5).sub.3 is used, an atactic 1,2-polybutadiene or an isotactic 1,2-polybutadiene is obtained, respectively [A. F. Halasa et al., J. Polym. Sci. Polym. Chem. Ed., 19, 1357 (1981); G. Natta et al., Chem. Ind. (Millan), 41, 1163 (1959)].
With the above catalyst systems, however, it is impossible to produce a cis-1,4-polybutadiene, a 1,2-polybutadiene having a desired vinyl content, a crystalline 1,2-polybutadiene and a polybutadiene containing crystalline 1,2-polybutadiene segments. That is, with the above catalyst systems, it is impossible to control the microstructure and stereoregurality over a wide range.
Further, the above catalyst systems have such problems that in producing a crystalline 1,2-polybutadiene, the catalyst activity is high in a halogenated hydrocarbon solvent but is low in a hydrocarbon solvent and the polymer obtained in a hydrocarbon solvent has a low melting point and a lower molecular weight than the practical level.